In a connector used for connection of electric wires of automobiles etc., a fitting type connection terminal composed of a combination of a male terminal and a female terminal is used. In recent years, electrical components have been mounted in the engine room of automobiles, and there is a need for the connector to ensure electrical characteristics (low contact resistance) after the lapse of a long time at high temperature.
When a copper alloy sheet strip with a surface coating layer, in which a Sn layer is formed as the surface coating layer on the outermost surface, is held over a long time under a high temperature environment, contact resistance increases. Meanwhile, for example, Patent Document 1 (JP 2004-68026 A as Patent Document 1 is incorporated by reference herein) discloses that a surface coating layer to be formed on a surface of a base material (copper alloy sheet strip) is provided with a three-layer structure of ground layer (made of Ni, etc.)/Cu—Sn alloy layer/Sn layer. According to the surface coating layer having this three-layer structure, a ground layer suppresses diffusion of Cu from the base material and a Cu—Sn alloy layer suppresses diffusion of the ground layer, whereby, low contact resistance can be maintained even after the lapse of a long time at high temperature.
Patent Documents 2 to 5 (JP 2006-77307 A as Patent Document 2, JP 2006-183068 A as Patent Document 3, JP 2007-258156 A as Patent Document 4 and JP 2013-185193 A as Patent Document 5) disclose a copper alloy sheet strip with a surface coating layer, including the above-mentioned surface coating layer having a three-layer structure, a Cu—Sn alloy layer being exposed on a surface. Of these, in Patent Documents 2 to 4, a base material having a surface subjected to a roughening treatment is used, and Patent Document 4 discloses Examples in which a Cu—Ni—Si-based alloy is used as a base material. In a copper alloy sheet strip with a surface coating layer disclosed in Patent Document 5, a Cu—Ni—Si-based alloy is used as a base material.
Patent Document 6 (JP 2010-168598 A as Patent Document 6 is incorporated by reference herein) discloses that, in a surface coating layer having a three-layer structure of Ni layer/Cu—Sn alloy layer/Sn layer, a Cu—Sn alloy layer is composed of two phases of a ε (Cu3Sn) phase at the Ni layer side and a η (Cu6Sn5) phase at the Sn phase side, and an area coating ratio of the ε phase, with which the Ni layer is coated, is adjusted to 60% or more. To obtain this surface coating layer, there is a need that a reflow treatment is composed of a heating step, a primary cooling step, and a secondary cooling step; and a temperature rise rate and a reaching temperature are precisely controlled in the heating step, a cooling rate and a cooling time are precisely controlled in the primary cooling step, and a cooling rate is precisely controlled in the secondary cooling step. Patent Document 6 discloses that this surface coating layer enables maintenance of low contact resistance even after the lapse of a long time at high temperature, and also enables prevention of peeling of the surface coating layer.
A Cu—Ni—Si-based copper alloy sheet strip disclosed, for example, in Patent Document 7 (JP 2008-196042 A as Patent Document 7 is incorporated by reference herein) is used as a base material which forms a surface coating layer whose outermost surface is a Sn layer. This copper alloy sheet strip has excellent bending workability, shear punchability and stress relaxation resistance, and a terminal formed from this copper alloy sheet strip is excellent in stress relaxation resistance, so that the terminal has high holding stress even after the lapse of a long time at high temperature, thus enabling maintenance of high electric reliability (low contact resistance).